1. Field of the Invention
This invention relates generally to an apparatus for producing thrust force reactions in an automatic transmission, particularly such forces due to transmitting torque between meshing helical gear teeth.
2. Description of the Prior Art
In an automatic transmission a planet pinion carrier supports a set of planet pinions, each member of the set being engaged with a sun gear and a ring gear. Typically, an axial force component, i.e., thrust load, produced due to the helix angle of the meshing gears and pinions and torque transmitted between them, is captured between the sun gear and the ring gear. Thrust load from the sun gear is directed at the ring gear hub, and the thrust load from the ring gear hub is directed at the sun gear. This allows the thrust loads to be cancelled, i.e., reacted by a force of equal magnitude and opposite direction.
Between the ring gear hub and the sun gear hub, a thrust needle bearing is typically used to react the thrust loads and handle the relative speed between the two components. Under coast load conditions, the planetary ring gear and sun gear may thrust apart from each other. Therefore, thrust from the ring and sun must be captured in both directions.
In some transmission applications, the speed differential between the ring gear and the sun gear is very high. That high speed differential across a thrust bearing causes significant frictional loss and adversely affects fuel economy.